Apparatus for electropolishing spherical surfaces



DBC. 15, w A A 3,547,796

APPARATUS FOR ELECTROPOLISHING SPHERICAL SURFACES Filed Dec. 24, 1968 INVENTOR. WILLIAM L. RANDALL A T TORNEY United States Patent US. Cl. 204213 4 Claims ABSTRACT OF THE DISCLOSURE Apparatus for rotating a sphere in an electropolishing bath in such a manner that every point on the surface of the sphere has equal average proximity to a cathode, While an electrical potential is constantly maintained between the rotating sphere and cathode. The apparatus thereby provides for size reduction of metallic spherical bodies Without loss of spherical trueness.

BACKGROUND OF THE INVENTION The invention disclosed herein was evolved under, or in, the course of Contract W7405ENG-48 with the US. Atomic Energy Commission.

Electropolishing is a polishing technique where an electric potental maintained between an anodic body composed of one element and cathode composed of another element, both immersed in a bath of suitable electrolytic solution, is effective to slowly dissolve the immersed surface of the anodic body and thereby highly polish same. The rate at which the anodic surface dissolves is governed by the electric potential between such surface and the cathode, as well as by the temperature of the electrolytic solution. However, the dissolution rate at any given point of the surface is dependent upon its distance from the cathode, i.e., the portions of the surface nearest the cathode dissolve faster than portions further away. Thus, the surface is not polished evenly unless all points thereof are at a constant distance from the cathode. Consequently, problems are posed in the electropolishing of spherical bodies without loss of spherical trueness, it being necessary that all points of the spherical surface be in equal proximity to the cathode. When spherical trueness can be maintained, electropolished spherical bodies are useful, for example, as ball bearings inasmuch as an electropolished surface has an increased wear resistance by virtue of the lack of surface stresses and burrs therein.

SUMMARY OF THE INVENTION The present invention relates to apparatus for electropolishing a spherical body without loss of spherical trueness, and is more particularly directed to simple apparatus for supporting a spherical body in an electropolishing bath and rotating same successively about randomly oriented axes so as to establish a substantially equal average proximity of every point on the surface of the body to a fixed cathode in the bath.

Apparatus in accordance with the invention basically includes a pair of rotatable vertically offset, open-ended drums having their rims in longitudinally spaced facing relationship to define a continuous rail with vertically offset support edges for supporting a spherical body during immersion in an electropolishing bath. Means are provided for establishing an electric potential between the supported spherical body and a fixed cathode immersed in the bath to thereby cause the body to gradually dissolve therein, Finally, provision is made to rotate the drums in opposite directions whereby the vertically offset rail support edges thereof impart rotation to the spherical body successively about randomly oriented axes and 3,547,796 Patented Dec. 15, 1970 maintain every point on the surface of the body in substantially equal average proximity to the cathode.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view of apparatus in accordance with the invention for electropolishing spherical surfaces.

FIG. 2 is a diagrammatic illustration depicting the motion of any given point of a spherical surface during the electropolishing operation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG, 1 in detail, electropolishing apparatus in accordance with the present invention will be seen to include a tray 11, or equivalent open-topped container, containing a suitable electrolytic solution which serves as an electropolishing bath 12. In order to facilitate electropolishing of the surface of a spherical body 13, means are provided for supporting the body in immersed position in the bath 12 in spaced relation to a cathode 14 also immersed in the bath. The cathode is preferably provided in the form of a metallic plate secured to the inner surface of one end wall of the tray 11. Upon the establishment of an electric potential between the spherical body 13 and the cathode 14, in a manner subsequently described, the body slowly dissolves in the bath and the surface of the body is electropolished in a well known manner.

In accordance with the particularly salient aspects of the invention, the spherical body support means are arranged to rotate the immersed body successively about randomly oriented axes such that the average proximity of every point on the surface of the body to the cathode is substantially the same. The spherical surface is thus uniformly electropolished and the spherical trueness of the body is maintained. More particularly, the support means comprise a pair of open-ended drums 16 and 17 respectively having circular hubs 18 and 19 with annular rims 21 and 22 projecting coaxially therefrom. The drums are mounted for rotation about parallel vertically offset axes lying in a common vertical plane With the respective rims 21 and 22 in opposed longitudinally spaced facing relationship. The rims define a continuous rail 23 with vertically offset support edges (i.e., the end edges of the inner peripheral walls of rims 21 and :22) for supporting the spherical body 13. The lower reaches of drum rotation extend beneath the surface of the bath 12 such that the body 13 as supported upon the rail 23 is immersed in the bath solution. In addition, means are provided to rotate the drums in mutually opposite directions.

The previously noted rotatable mounting of the drums 16 and 17 is preferably facilitated. by means of shafts 24 and 26 respectively projecting coaxially from drum hubs 18 and 19 and extending through appropriately positioned bearing plates 27 and 28 provided at the opposite end Walls of the tray 11. At least one drum 16 is arranged to be selectively slidable along its associated shaft 24 in order that it may be backed away from the other drum sufiiciently to permit introduction of the spherical body 13 to the drum interiors for support on the rail 23. To this end, drum 16 may be provided with a boss 29 having a set screw 31 threaded radially therethrough into engagement with the shaft 24. The drum may consequently be selectively released for slidable translation along the shaft.

The means for rotating the drums 16 and 17 in mutually opposite directions may advantageously comprise a simple belt and pulley power transmission system coupling a motor 32, mounted on a side wall of the tray 11, in driving relation to the drums. More particularly, the motor is provided with a rotary drive shaft 33 which extends from both ends of the motor housing and is parallel to the shafts 24 and 26. Pulleys 34! and 36 are coaxially secured to the opposite ends of drive shaft 33, while pulleys 37 and 38 are coaxially secured to the free ends of drum shafts 24 and 26. A forward rotation drive belt 39 is engaged about pulleys 34 and 37, whereas a twisted, or figure-8, reverse rotation drive belt 41 is engaged about pulleys 36 and 38 to thereby effect rotation of the drums in mutually opposite directions. It will be appreciated that numerous alternatives to the foregoing arrangement are possible to drive the drums in opposite directions.

The establishment of an electrical potential between the spherical body 13 and cathode 14 may be effected as by means of a direct current power supply 42 having positive and negative terminals 43 and 44 respectively coupled to the drums 16 and 17, and to the cathode. In this regard, the drums 16 and 17 and drum shafts 24 and 26 are preferably of electrically conducting material while the tray 11 is of non-conducting material so as to insulate the cathode from the drums. Brushes 46 and 47 secured to opposite end walls of the tank and slidably engaging the drum shafts 24 and 26 may then be connected to terminal 43 of supply 42 to apply positive potential to the drums and hence to the supported spherical body in electrical contact therewith, The cathode is connected directly to the negative supply terminal 44, and the previously noted electric potential is thus established between the spherical body and cathode.

In summary, with the spherical body 13 supported in immersed position in the bath 12 upon the continuous rail 23 defined by the oppositely rotating drums 16 and 17, and electric potential established between the body and the cathode 14, the body gradually dissolves in the bath and the body surface is electropolished in a well known manner. By virtue of the vertically offset support edges of the support rail afforded by the vertically olfset drums, and the drums being rotated in mutually opposite directions, rotation is imparted to the spherical body in such a manner that the path of motion of any given point on the surface of the body is substantially as depicted in FIG. 2. In this regard, it is to be noted that the point describes randomly oriented open and closed helical curves. In other words, the spherical body is successively oriented about randomly oriented axes and all points on the body surface consequently have essentially equal average proximity to the cathode 14. The body is dissolved uniformly over its entire surface during the electropolishing process and spherical trueness is thus maintained.

What is claimed is:

1. Apparatus for electropolishing spherical bodies comprising container means adapted to contain an electro- 50 polishing bath, a cathode immersed in said bath, a pair of rotatable vertically offset drums having rims with open ends disposed in longitudinally spaced facing relationship to define a continuous rail for supporting a spherical body in immersed position in said bath, means for establishing an electric potential between said spherical body and said cathode, and means for rotating said drums in mutually opposite directions to successively rotate said spherical body supported on said rail about randomly oriented axes whereby all points on the surface of said body are maintained in substantially equal proximity to said cathode.

2. Apparatus according to claim 1, further defined by said drums having shafts respectively projecting coaxially therefrom mounted for rotation in opposite end walls of said container means, and said means for establishing an electric potential including a pair of brushes respectively slidably engaging said shafts, and a direct current power supply having a positive terminal connected to said brushes and a negative terminal connected to said cathode, said drums and shafts being of electrically conducting material.

3. Apparatus according to claim 2, further defined by said means for rotating said drums comprising a motor secured to said container means and having a rotary drive shaft in parallel relation to said drum shafts, a first and second pulley coaxially secured to said drive shaft, third and fourth pulleys respectively coaxially secured to said drum shafts, a forward rotation drive belt engaged about said first and third pulleys, and a figure-8 reverse rotation drive belt engaged about said second and fourth pulleys.

4. Apparatus according to claim 2 or 3 further defined by one of said drums being selectively slidable along its associated shaft,

References Cited UNITED STATES PATENTS 1,916,492 7/ 1933 Schuricht 20421.2 2,390,282 12/1945 Tour et a1 204212 2,549,946 4/1951 Treuhaft 20'4140.5 2,645,611 7/1953 Axtell .204.5 2,963,772 12/1960 Niles, Sr 29-l48.4 3,088,783 5/1963 Conover 30835 3,161,578 12/1964 Facquet et al. 204-212 3,244,613 4/ 1966 Karlquist .204212 3,272,729 9/1966 Jumen 2042l3 JOHN H. MACK, Primary Examiner T. TUFARIELLO, Assistant Examiner US. Cl. X.R. 204 -1405 

